1. Field of the Invention
This invention relates generally to valves used in internal combustion engines and, more particularly, to overhead valves especially shaped to enhance fuel and air mixing for improved combustion efficiency and engine performance.
2. Description of the Related Art
Internal combustion engines are well known in a wide variety of configurations and applications. A long series of refinements have been applied in efforts to improve the performance of such engines. Much attention has been focused on improving the efficiency of combustion of the fuel and air mixture within the cylinder's combustion chamber.
A number of approaches have been tried in order to obtain increased engine performance, either alone or in combination. Specially shaped combustion chambers, increased number of valves per cylinder, specially shaped piston faces, and a wide variety of spark plug positions and configurations have all been explored and used with varying degrees of success.
Since the invention of the internal combustion engine, a significant amount of attention has been directed to the improvement of valve design. The valves that control the flow of the intake and exhaust charges in most engines are of the poppet type, which means that they move in and out of the valve ports in order to open and close the passage. During operation of the conventional internal combustion engine, cams on a rotating camshaft operate to lift the tappets, which in turn lift the pushrods and actuate the rocker arms, which push down on the tips of the valves. When this happens, the valves are lifted off their seats and allow either intake or exhaust gases to flow in or out of the combustion chamber.
In efforts to improve airflow into and out of the combustion chamber, various aspects of the valves have been modified in a variety of ways. Many of these valve shape modifications affect engine performance, but no one particular design necessarily performs better than another. Rather, a particular valve design complements a given port of a given head in order to produce the best flow. For example, Chrysler's famous "Hemi" engine incorporated a valve that resembled a tulip bulb at the valve fillet. It was Chrysler's opinion that this shape maximized flow through the intake ports of the heads used on those engines.
Various valve designs have addressed different portions or features of the overall valve. The angle of the valve face and the angle of the valve seat have frequently been varied, either independently or in cooperation. "Top cut" angles and "bottom cut" angles on either side of the valve seat formed in the engine head have been varied to improve performance. Valve stems have been "necked down" in the portion of the stem that will occupy the port, in order to reduce flow restriction and, further, to reduce slightly the weight of the valve. Stem lengths have been varied in order to accommodate different engine head thicknesses or to avoid coil bind in the valve spring. The height of the valve margin, or thickness of the valve head, has also been varied in efforts to improve flow.
As can be discerned from the above discussion, much time and effort have been directed to improve flow past engine valves. Other efforts have been directed at designing improved piston faces that will "swirl" the contents of the combustion chamber during the compression stroke and thereby improve combustion efficiency. Spark plug position and spark plug design have also been used to improve efficiency of combustion.